Telephone system



Aug. 29, 1933. M. E. GRlFr-'lNs TELEPHONE SYSTEM Filed Feb. 12. 1932 2 Sheets-Sheet 2 LAS @virs Iam *TWG

uf no .l1-Turris E. Erm 'ms Patented Aug. 29, 1933 PATENT;- oFFici: v

UNITED STATES vTELEPI'IONE SYSTEM Morris E. Grilins, Chicago,`: Ill., assigner, by

mesne assignments, to vAssociated Electric Laboratories, Inc., Chicago, Ill., a Corporation of Delaware Application February 12, 1932. Serial No. 592,455 12 claims. l(o1. 179-27) This invention relates to telephone systems in general, and, particularly, to multi-oce tele-V General description i As is well known, it is desirable, when practical, to provide a single, large group of trunks or switches rather than several small groups due to the resultant increase in efficiency. y In Acase traffic from lines with diilerent service requirements is routed over such trunk or switch groups, there must necessarily be arrangements for distinguishing between the differentA classes of lines so that the particular service requirements of each line can be met. As an example, an automatic oflice in which both paystation lines and regular or flat-rate linesterminate may be'provided with a single group of trunks extending to the toll switchboard. If there are a large number of lines in each class, separate switch trains may be provided for the various classes and connectionsmay be extended to the toll trunks overY diiferent routes. This arrangement, however, is ineflicient when the line groups involved are relatively small, and under these conditions it has beenthe usual practice to associate identifying means (usually tone apparatus) with the lines. An arrangement of this type is disclosed in the copending application of V. S. Tharp, Serial No. 512,047, filed January 29, 1931, on which Patent No. 1,868,956 was granted July 26, 1932, in which a tone source at a lineswitch is adapted to be connected through to a trunk by way of the vrelease trunk or holding conductor. This arrangement involves the provision of special tone circuits for the lineswitch units, thereby adding to their cost, and, what is more objectionable, the tone applied to the release trunk conductor, which is included in the cable with the talking conductors, may induce disturbing currents in adjacent talking circuits unless special precautions are taken to prevent it. In the present invention, the objectionable featuresv above mentioned are entirely eliminated by applying the tone to the toll trunks at the trunk repeaters. Further, provision is made for distinguishing between the lines of different classes without increasing the number of conductors in the local trunks extending from the selector banks to the trunk repeaters. This constitutes one of the features of the invention.-

The foregoing dicussion deals generallywith the problem of signalling ahead as to the character'of a calling line. In addition, there is the problem of vbackward signalling when the lines involved have different requirements as to supervision. As a ,further example, the automatic oce above discussed may serve as a tandem Y..

switching point for a manual office not directly connected with the toll switchboard. In this case also, aspecial switch train and separate route of access tothe toll trunks could be provided lfor c alls from the manual oiiice, but this would be impractical if there were only a few manual oiice trunks.. The present invention, therefore, contemplates the routing of calls from the manual oilice over the same switch train and trunk group that is used for calls originating inthe automatic oiiice, and provision is made for givingY the'ki'nd of supervision required inY each case. This ar-y rangement constitutes another feature of the invention..

Description of drawings y The accompanying drawings comprising Figs.

1 and 2 show one embodiment of the invention. Fig. 1 shows switching apparatus located in an automatic office. Fig. 2 shows a toll trunkand associated equipment connecting the automatic oflice with a toll switchboard.

Referring to Fig. 1, there is shown a paystation line PS, a trunk line T, and a subscribers line A;

terminating, respectively, in lineswitches LS,

LS1, and LS2. VThe lineswitches haveaccess in common. to a number of rst selectors, such as selector S. The paystation line, which is of the postpay type, may be similar to that disclosed in ther cofpending application of` T. C. Riebe, Serial No. 344,689, filed March 6,1929 on which Patent No. 1,844,684 was granted Feb. 9, 1932.

Only4 the essential features of the coin-control apparatus have been shown in detail.V Lineswitch LS has been shown for convenience as an ordinary rotary-type lineswitch, although any other suitable type of lineswitch orV line finder may be used. The lineswitch is equipped with a discriminating wiper in Vaddition to the usual line and test wipers, anda pair of terminals-are provided for facilitating the connection of ground 'to the extra wiper in orderto identify the class Selector S, also shown in Fig. 1, is a twomotion, Strowger-type selector. This switch is generally similar to the usual selectors except that additional contacts and a set of shaft springs have been provided for purposes to be described later. This selector, with other similar selectors, has accessover certain levels of its bank to trunks extending to the next rank of local switches, and on a different level of its banks access is had to trunks extending to the toll switchboard. The shaft springs, above mentioned, are adjusted to operate when the shaft and Wipers are raised tovthe'level in which the trunks to the switchboard terminate.

Referring now to Fig. 2, there is shown a trunk line T1 extending from the automatic cnice in which the apparatus of Fig. 1 is located to a toll switchboard located in a distant office. Repeater R is a trunk repeater of the same general type as that disclosed in theTharp application previously referred to. A differential relay connected in 'series with the line relay controls the variousV disc irninating" functions, such as classV signalling and supervision. The repeater is provided with the usual means for automatically removing tone lfrom'the trunk after the'operator Aemswers the call. Supervision is given by current reversal in connections where itis required. The trunk line is arranged for two-way service, and, accordingly, an incoming selector is provided in connection with the repeater R. The trunks terminate at the switchboard in the usual line f relay group L with which cord circuits of any primary winding ci" suitable type may be used for answering and extendinggcalls. One such cord circuit C has been shown in part for convenience of description.

Y Detailed description Y Having briefly described the invention and certain of its more prominent ie tures, the operations involved in setting up connections in a systemfembodying the same will now be described in detail. A connection from paystation line PS to the toll switchboard. will be considered first. 'When the receiver is lifted at the station to initiate a call, a circuit for line relay la of the lineswitch may ce traced from battery, winding of the relay, contacts 15, line conductor l, righthand winding of polarized relay 3, branch conf jductjor 4, switchhook spring contacts 39, vimpulse contacts 6 of the calling device CD, transmitter,

induction coil 5, line conductor 2, andcontacts 22, to ground. VRelay 14 operaties and closes the usual testing and busying circuits at contacts 23 and 2li. The connection of ground to conductor 3Q marks the callingr line busy in the banks of the connectors. The lineswitch now proceeds to test the trunk on which its Wipers are standing, and, if this is busy, steps ahead in the usual Way in search of idle trunk. When an idle 'trunk is found, forexample the trunk terminating on selector S, relay 13 operates, opens the circuitof relay 14 at contacts 16 and 22, switches the test wiper over from testing Ato holdingposition'by opening contacts 18 and 'closing contacts19, connects ground by way of contacts 20 to discriminating wiper 28, and at contacts 17 and 21 connects line conductors 1 and Y2 by wayof wipers 25 and 23 and branch conductors 31 and 3s to conductors 35 and 38 ofthe trunk. Relay l/l lis slow to release and maintains relayflB operated until ground is returned on the release-trunk conductor from the selector. In the selector, relay 52, which is bridged across the trunk conductors by way of contacts 65 Vand 72, operates over the calling subscribers loop and completes a circuit for relay 53 atcontacts 73. Relay 53 operates, prepares the impulsing circuit at contacts 75, and applies ground to releasetrunk conductor 36 at contacts 50.

It will benoted that a winding of polarized magnet 3 is included in the operating circuit of the line relay of the selector The magnet does notV operate at this time due to the direction of current flow in its winding. The calling scriber now dialsthe Adigit designating the operators position, for example the digit 0, and the circuit of relay 52 is interrupted accordingly at impulse contacts 6 of the calling device. Relay 52 responds by deenergizing and reenergizing, and transmits a like series'of impulses by way'of contacts'll and 75, windings of relay 54 and vertical magnet 56, to battery. The magnet operates in response to each impulse and raises the shaft andwipers opposite the-level-inwhich the toll trunks are accessible. Relay 5f; operates in series withvthe magnet, and,rdue to' its slow-releasing characteristic, remains `operated throughoutV the series of impulses, On the first vertical steprof the wipers the circuit is closed from ground at contacts 50, contacts 7S, offnormal contact 6), relay 55, to battery. Relay 55 completes a lool;- ing circuit for itself at contacts 31 and prepares a circuit for therotary magnet at contacts 50,

Shortly after the last impulse of the-series, relayV ict V5l restores, opens the original energizing circuit Y stores vupon the operation of the rotarymagnet due to the opening of lits circuit at interruptor contacts 79. The reoperation of relay V55results in the reclosure of the circuit of the rotaryv magnet and the wipers advance another step. These operations are repeated `until an idle trunlrlis found, which, for convenience, maybe assumed to be thertrunk comprising conductors 35--37, f

extending to repeater R. This t unk being idle, .the test wiper of the selector finds no busy mark- Ying ground on the test contact, and relay 55 does not` operate. Further, ifV there is no ground on the test wiper, relay 51 is no longer shunted and operates over Va circuit including ground at contacts 50, cam spring contacts 59, winding of relay 51, interrupter contacts 79, off-normal contacts 60, winding of relay 55, to battery. Relay 55 does not operate dueto the high resistance of relay 5l. Relay 5l opens the circuit of relay 52 at contacts 65 and 72, extends the calling subscribers loop through vto the repeater at contacts 66 and 71, opens the original test circuit and prepares a holding circuit for itself by opening Vcontacts 67 will release after a short interval, It will be recalled that the shaft springs are adjustedl to .operate when the Wipers of the switch are raised to the level in which the toll trunks are accessible. As this is the case in the present instance, conreleases and opens the circuit of relay 573 which LS, strap 21, vcontacts 20, wiper 28, branch conductor 33, trunk conductor 37, shaft spring contacts 64, and contacts 70 and 88. The purpose of this momentaryV application of ground will become apparent when the operation of the revpeater is considered.

rReferring now to the repeater, the switching througlfiV of the selector as above described eX- tends the calling subscribers loop by way of conductors 85 and 87, contacts 110 and 115,l contacts 120 and 125, upper and lower windings of differential relay 104, upper and lower windings of relay 105, to battery and ground. Relay 105 operates and completes a circut for relay 102 at contacts 128. It will be recalled thatin thev connection under consideration the selector after switching through momentarily applies ground via thediscrirninating conductor to the'lower'side of the trunk. This ground connection shunts the lower windings of relays 104 and 105, thereby permitting relay 104 to energize over its upper winding-alone. Relay 104 completes a circuit for relay 103 at contacts 127. Relay 103 operates,

connects the trunk conductors directly to relays 104 and 105, independent of the reversing contacts, of relay 101 by opening contacts 120 and 125 and closing contacts 121 and 126. Relay 103 also completes a holding circuit for itself at contacts 122, removes the normal ground connection from the'lower winding of battery-feed relay 101 y at contacts 124, and at contacts 123 connects the relay'winding through to ground on which a tone isfsuperimposed. Asa further result of the 'opjjj; eration'of relay 102, parallel circuits are corn-A pleted for relays 108 and 109, the circuit of the former relay extending over contacts 119 and 142 and that of the latter relay over contacts 119 and 144. Relay 109 operates, disconnects the out- {45g going trunk conductors from the incoming switch at contacts 148-and 153 Vcomiects ground to the upper trunk conductor at contacts 149, completes a locking circuit for itself at contacts 150, applies ring-back' tone to the lower talking conductor of the repeater 'at contacts v151, and at contacts 152 connects Vthe'generator to the lower outgoingl trunk conduictor.4 Relay 103 energizes at this time, but its single spring is weighted at `one end and' the springl accordingly vibratesr and prevents the closure of contacts 147 for a long 6110112511 vcontacts 162 and 166. .During the interval in which rringing current is transmitted over the trunk the spring of relay 108 is vibrating. After a certain definite intervaLthe vibration ceases and the springs corne to rest with contacts 147 closed. Relay 107 accordingly energizes in parallel with relay 103 and locks to ground by way of contacts 143 and 119. Relay 107 disconnects the trunkconductors from the ringing circuit at contacts 137 and 146, and at contacts 138 and 145 extends these conductors through to the talking condensers and battery-feed relay of the repeater. A circuit is prepared for relay 106 at contacts 139, the original energizing circuit of relay 108 is opened at contacts 142, a new circuit is prepared for this relay at contacts 141, and the original energizing circuit of relay 109 is opened at contacts 144. Relay 108 restores but relay 109 remains energized over-a locking circuitk including contacts 150, 114, and 119. The subscriber is now receiving ring-back-tone to indicate that the operator is being. signalled, and lamp L glows to notify the' operator of the incoming call.

' The operator answers the call by inserting the plug P of Y a cord circuit vC into `iack J, thereby completing a circuit for relays 160 and 167Y in series over the sleeves of the plug and jack. Relay 160 opens the circuit of lamp L at contacts 163, closes an additional circuit for the lvisual signal at contacts 164, disconnects the upper winding of relay 159 from the trunk at contacts 174 and 165, andv opens the circuit of the lower winding of relay 159 at contacts 166. Relay 159 restores. Battery-feed relay 101 of the repeater now operates over a circuit which may be traced from battery, upper winding of the relay, contacts 132 and` 145, trunk conductor 158, ring contacts of the jack and plug, supervisory relay 168 be audible to the operator who will have connected her telephone set to the cord circuit. The

tone willV indicate the character of the calling line. The operation ofrelay 101 as described results in the completion of an additional circuit for relay 102 at contacts 112, the opening ofthe holding circuit of relay 109 at contacts 114, and

the closure of a new circuit for relay`108 by wayV of contacts 119, 113, and 141. It may be pointed out at this time that relay 101 on operating also actuates reversing contacts-110, 111, 115, and 116, but without effect in this particular connection due to the previous operation of relay 103 which by-passed the reversing contacts. Relay 108 again energizes, and its weighted spring vibrates as before. After an interval, the 'spring comes yto rest and a circuit is completed` by way of contacts 147 and 139 lfor relay 106. Relay 106 is slow-to-operate, and after an interval energizes, short-circuits the two windings of differential relay 104 by closing contacts 133 and 134, removes vthe tone ground from the lower winding of relay-101 at contacts 135, and connects direct ground to this relay at contacts'136. Relay 108 accordingly will remain'operated as long as relay 101 is energized and the tone will be cleared-from the trunk. In case the operator wishes to recheck the line, the tone may be reapplied to the trunk by momentarily withdrawing the plug from the jack. y

The operator may now converse with the calling party and further extend the call as required. As there is no reversal of battery over the trunk comprising conductors 85-87, polarized magnet 3 of the paystation equipment is not operated,

and the talking circuit is not interrupted. Any

necessary charges will be made under thcsupervision of the operator, that is, the calling subnow be described. Upon the extension of the call scribers coin will actuate an audible signal in the usual manner to inform the operator as to the amount deposited. Y i

When the calling subscriber hangs up at lth termination of the call, the loop circuit over which relay 105 of the repeater has been'energized is opened and the relay restores. Relay 1,05 opens one point in the circuit of relay 102 at contacts 128, but this relay is now held operated over a circuit including contacts 112. Relay 105 also reverses the connection of relay 101 to the outgoing trunk conductors by opening contacts 130 and 132 and closing contacts 129 and 131. The reversal of current flow over the trunk line energizes the polarized relay 168 of the cord circuit, which completes a circuit for supervisory lamp L1 at contacts 173. The operator may now release the connection by withdrawing the plug of the cord from the jack. This operation opens the circuit of relay 101, which restores, and opens the circuit of relay 102. Relay 102 restores, removes the ground from release trunk conductor 86 at contacts 118 and at contacts 119 opens the holding circuit of relays 10,6, 107, and 108. These relays restore and the repeater is ready to receive the next call. The removal of ground from release trunk conductor permits selector S and lineswitch LS to restore in the usual way. Y

The operation of the paystation line apparatus in calls to local subscribers in the automatic exchange is not particularly concerned with the present invention and will not be described in detail. It may be pointed out, however, that in connections or" this type, the selector is operated-to connect with the trunk on one of the local levels and the shaft springs are not operated. The discriminating conductor accordingly is not con- `nected to the local trunk and the connection is extended in the usual way. Upon the call being answered, the connector reverses battery to operate the polarizedrnagnet of the paystation apparatus which disables the talking circuit at that station. rllhe calling subscriber then deposits the necessary coin and the talking circuit is coinpleted as described in the previously-mentioned Riebe application.

The establishment of connection from the manual cnice over trunk T to the toll switchboard will over trunk T, lineswitch LS1 operates in the same manner as described for lineswitch LS, and the trunk is extended to an idle rst selector, for example the selector S. 1t will be recalled that the discriminating wiper of this particular lineswitch is not grounded, which is the distinguishing characteristic of this line. The selector is operated to the level in which the trunks to repeaters such as R are accessible, and selects an idle trunk in the same manner as described for the previous ccnnection. The operation of the shaft springs at this time is without eiiect as there is no ground on the discriminating conductor. The line relay of the repeater operates as before but differential relay 104 does not operate in this connection since there is no ground connection to the lower trunk conductor. Relay 103 accordingly is not operated in connections of this kind, and the reversing contacts of relay 101 are eiective to reverse the connection of relay 105 to the incoming trunk upon the answering of the call. Further, no tone is applied'to the lower winding of relay 101 and the absence of this tone informs the answering toll operator of the character of the calling line.

Ringing current is applied to the line as in the previous connections, and the talking circuit is completed upon the operation of relay 107.V Relay 101 operates when the call is answered andby opening contacts 110 and 115 and closing contacts 111 and 116 the direction of current flow is re- Calls from flat rate stations in the automatic:

exchange such as from the station A are completed over lineswitch LS2, a selector S, and a repeater R, in the same manner as calls over the trunk T. The lineswitches for lines of this class are also characterized by the absence of ground on the discriminating wiper, and the repeater accordingly reverses battery when the call is answered. This battery reversal'may be used for operating a meter or for other purposes which arewell known.

incoming calls from the toll switchboard to the automatic exchange may be extended over the trunk T1 by means or a dialling cord circuit (not shown), an incoming selector, and the local switches or the automatic oliice. The line relay of the incoming selector is bridged across conductors 15e and 156 and controls the operation of the selector' in the usual way. The release relay or the selector returns ground over release trunk conductor 155, which marks the trunk busy in the banks of the selectors, such as selector S, and thereby guards the trunk against'intrusion during incoming calls.

What is claimed is:

1. 1n a telephone system, a repeater, atrunk terminating in the repeater, means for extending calls from lines of a plurality of classes over said trunk and through said repeater, means for answering the calls, means in the repeater normally eiective to reverse the direction of' current ow over the trunk responsive to theV answering of a call, and means in the repeater operated'responsive to the extension of a call ltherethrough from a line of one of said classes for preventing the operation of said last means.

2. In a telephone system, a local trunk'and an outgoing trunk connected by a repeater, means for extending calls. from lines ora plurality of classes over said trunks and said ref'peatcnl means in the repeater normally -effective to reverse the direction of current flow over said local trunk responsive to control'over said outgoing trunk, `and means in the repeater controlled over said local trunk and dependent'on the class of the calling line for rendering said last means ineffective.

k8. In a repeating device, *a pair of incoming conductors, a relay bridged across said conductors, a second relay ncrmallyeective onoperating to reverse the connection of the rst relay to said conductors, a third relay controlled over said conductors, and means controlled by said third relay for preventing said secc-nd relay from eiecting the reversal of the rst relay connections.

4. In a telephone system, a trunk terminating in a repeater, three relays, circuit connections including contacts of the rst relay connecting the second relay to the trunk, other circuit connections including contacts of the third relay for connecting the second relay to the trunk independent o said first circuit connections, means for seizing the trunk in connectionsA of two classes,y and means automatically operated in calls of one class for operating said third relay.

5. In a telephone system, a repeater, a trunk incoming to the repeater, a relay in the repeater bridged across the conductors of the trunk, a second relay in the repeater normallyefective to reverse the connection of said first relayrto the trunk conductors, means for seizing the trunk to extend calls of various classes through the repeater, means for momentarily unbalancingA the trunk responsive to its seizure to extend a call of one particular class, and means in the repeater operated responsive to the unbalancing of the trunk for preventing said second relay from reversing the connection of .said rst relay to the trunk conductors.

6. In a telephone system, a local trunk and anA outgoing trunk connected by the repeater, means for extending calls from lines of a plurality `of classes over said trunks and said repeater, means for answering the calls, means in the repeater responsive to the answering of a call extended from certain of said lines for reversing the direction of current flow over the local trunk, and means responsive to the extension Vof calls from other of said lines for applying a distinctive tone to the outgoing trunk and for preventing the reversal of current ilow over the local trunk upon such calls being answered.

'7. In a telephone system, a local trunk and an outgoing trunk connected by a repeater, means for extending calls from lines of various classes over said trunks and said repeater, means for answering the calls, reversing means responsive tothe answering of calls extended from certain of said lines for reversing the direction of current iiow over the local trunk, means responsive to the extension of calls from other of said lines for connecting a tone source to the trunk line, and means responsive to the answering ot calls from said other lines for disconnecting said tone source from the outgoing trunk and for operating said reversing means without reversing the direction of current ow over the local trunk.

8. In a.` selector switch, an incoming trunk comprising talking conductors, a test conductor and a discriminating conductor, means controlled over said talking conductors for setting the selector, contacts operated dependent on a particular setting of the selector, and means including said contacts for momentarily connecting said discriminating conductor to one of said talking conductors.

9. In a telephone system, an automatic switch, means for directively operating the switch to select a group of outlets, means for automatically operating the switch to select an idle outlet in the group, and means dependent on the eX- tent of the directive operation of the switch for momentarily placing a distinctive electrical condition on the selected outlet.

10. In a telephone system, an automatic switch, means for extending calls from lines of two classes to said switch, means for directively operating the switch to select a group of outlets, automaticl means for further operating the switch to select an idle outlet in said group, and means dependent jointly on the class ofthe calling line and on the extent of the directive opertion of the switch for momentarily placing a distinctive electrical condition on the selected outlet.

11. In a telephone system, an automatic switch, a trunk comprisingftwo talking conductors, a test conductor and an auxiliary conductor terminating in said switch, outlets each comprising two talking conductors and a test conductor accessible to said switch, means for extending a connection over said trunk to said switch, means for directively setting the switch in selective relation -to a group of outlets, means for operating the switch to select an'idle outlet in said group, and means dependent on the particular setting of the switch for momentarily connecti'ng the auxiliary conductor of said trunk to a talking conductor of the selected outlet.

l2. A telephone system as claimed in claim 11 in which connections from lines of two classes are extended to the switch over the trunk and in which the class to which aline belongs is indicated by the presence or absence of a potential onthe auxiliary conductor of the trunk. 

